1. Field of the Invention
The present invention relates to a split wedge/breech block design for use in guns that develop high pressures upon firing, as well as to a sealing means for such guns.
2. Description of the Prior Art
The development of the XM 297 cannon system created sealing problems between mating cylinders which previously were not employed in similar guns. The 155 mm XM 297 cannon system creates pressures that vary from 5,000-65,000 psi with a total operating pressure impulse of approximately 25 milliseconds. The propellant used in the XM 297 gun system produces a high temperature, high pressure, corrosive environment. In order to overcome these extreme environmental conditions, the XM 297 gun seal has to be capable of responding to quick pressurize times and must be environmentally inert. The seal also has to be capable of withstanding the vibratory action associated with the XM 297 system.
The problem of sealing the interface between two mating cylinders was observed in the early test firing of the XM 297 gun. After initial testing, it was found that the prior art seal was missing or damaged by approximately 60 firings of the gun at low pressures. Such prior art seals were designed for a limited number of low pressure firings where the seal was readily accessible for replacement. A novel bridge seal was developed for this purpose and is disclosed in copending application Ser. No. 08/019,494, filed Feb. 16, 1993; Ser. No. 08/371,638 filed Jan. 12, 1995, and Ser. No. 08/540,111 filed Oct. 6, 1995.
Once the concept of a bridge sealing means was developed, it became necessary to develop a breechblock design for the purpose of inserting and extracting the new bridge seal from the powder chamber of the gun tube. Again, due to the novel type of sealing means employed in the XM 297 gun, this problem was not faced in prior art gun systems.
The split wedge/breech block design was developed with the knowledge that very little linear motion would be required to extract the bridge seal from the powder chamber of the gun tube. The split wedge/breechblock divided the breechblock into two parts slidably movable relative to one another. However, the development of the split wedge/breechblock design posed an additional problem, namely that a high pressure face seal was required to seal the two sliding flat surfaces of the wedge and breech block. A seal was needed which would accommodate two sliding surfaces and at the same time not be destroyed due to the reciprocating motion of the surfaces and the harsh conditions encountered in the gun.
Finally, it was discovered that under high pressure operation, the split wedge/breech block design could lead to an adverse downward force upon firing of the gun, which force was created by the wedge angle. This is because the force transmitted through the system (wedge, block and breechring) was not normal to the surfaces thereby creating a downward force when firing. As a result of this discovery, a more preferred version of the split wedge/breechblock design was developed to insert and extract the bridge seal. In the more preferred design, the motion of the split wedge/breechblock design is duplicated but stepped faces are employed in place of angular surfaces in order to ensure that the forces exerted by firing the gun are normal to the surfaces of the wedge and breechblock thereby eliminating the downward force which was generated during firing.